Radio locating equipment



Dec. 28, 1948 3 H. F. MAYER RADIO LOCATING EQUIPMENT 3 Sheets-Sheet 1 Original Filed Nov. 50, 1943 TRANfillizl TRIGGER AMP.

LIF'PER AMP.

SWEEP l C TIMING MV,

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Inventof:

Harry F. Mayer,

HIS Attorney Dec. 28, 1948.

H. F. MAYER RADIO LOCATING EQUIPMENT Original Filed NOV. 50, 1943 3 Sheets-Sheet 2 Fig.2. 7 r

TRANS 2 J\I m F| r M 22$ QEFl-"i'fii? 3 f I 15' I8 u I SWEEP Inventor Harry F. Mayer,

Hi ttorney.

Dec. 28, 1948. y 12,457,580

RADIO LOCATING EQUIPMENT Original Filed Nov. so, 1943 Y SSheecs-Shee1;3v

Inventor:

W H67 1 y F. Mayer,

y HiZZ-Jtorney.

Patented Dec. 28 1948 BABES LOfiATllNG EQUIPMENT Harry F. Mayer, Schenectady, N. Y assignor to General Electric Gompany, a corporation of New York Original application November 30, 1943, Serial No.

Divided and this application December 26, 1944;, Eerie-1N0. 569,740

5 {ll-aims. 1

The present invention relates to radio locating equipment for determining the range of remote objects by the time of travel of pulses of radio waves and is particularly concernedwith circuits for producing synchronized oscillations utilized in providing a time (range) scale.

This is a divisionof my copendi-n'g-application' Serial No. 512,301, filed November30j1943 and assigned to the-same assignee as the present invention.

An objectof my invention is to provide an improved c-ircuit for producing synchronizedtiming oscillations.

The novel features which-I believe to be characteristic cf'my invention are set forth with par ticularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by' reference to the following description taken in connection with the accompanying drawing in which Figs. 1 and "2 are circuit diagrams of equipment embodying-my invention, Figs. 3 and 4 are explanatory diagrams illustrating the operation thereof, and-Fig; '5 isa circuit diagram of a delay-or swee-p"timing'multivibrator of a type useful in equipment according to my invention.

Referring to Fig. 1 of the drawings, there is shown radio locating equipment having a direc tionalantenna l connected to a'transmitter 2 keyed by a pulse-r 3 to'transmit-directional pulses of radio Waves at the desired repetition rate. The antenna is also connected to a receiver lthrough a TB box 5 which limits the amplitude of the pulses appearing atthe'antennain such a manner as to prevent injury to the receiver by the transmitted pulses and without offering any substantial resistance tothe echoes of the transmitted pulses. The receiver output is fed through a switch 6 and a pulse amplifier 1 to the center electrode 8 of a circular sweep cathode ray tube 9 having a beam deflected in a circular path by A. C. sweep voltages 9.0 degrees out of phase ap plied respectively to the, vertical and horizontal deflection plates ill and H in a manner hereinafter described. "The receiver output which consists of transmitted pulses and echoes arriving after intervals corresponding. to the range" of the ,refiect'ingobjectscauses radial deflections of the beam which appear on the cathode ray tube viewing screen at. l2. and it. The range of the reflecting objects can. be. determined by angular distance between the deflection .l-icorrespondin to the transmitted pulses and the deflections 53 corresponding to the echoes.

It is obvious that the accuracy of the range determination is directly dependent upon the frequency and relative amplitudes of the sweep voltages applied to the deflection plates It! and it. Furthermore, the sweep voltages should be syn chronized with (i. e., have a definite time phase with respect to) the transmitted pulses so that the starting point of the circular sweep trace (1. e., the zero range point indicated by the deflection l2) will-remain fixed on the cathode ray tube viewing screen. This is essential not only for determining the range of the reflecting objects but also for distinguishing the echoes from the non-synchronous noiservoltages causing the erratio deflections-si t intermediate the deflections 2 and iii; it isa'also desirable that the pulse frequency of the transmitter be variable independent of the sweep'ifrequency so as to prevent synchronous interference due to simultaneous operation of more than one equipment in the same locality.

Inth-e"presenttequipmcnt"the independent adjustmentsare-obtained byusing .a pulse frequency multivilorator 1-5: to. initiate the pulse transinission and the generation of the sweep Voltages. Because the multivibrator is utilized to initiate these operations the pulse frequency and the frequency of the sweep voltages can be independently'varied.v The leading edge of the pulse frequency multivibrator output, shown in line A of Fig. 3; fires a delay multivibratorit having an output shown in line Dof Fig. 3. The delay multivilorator may comprisea circuit of the type show-n on peg-e158 of Reference Data for Radio Engineers published by, the Federal Telephone and Radio Corporation, copyright 1943. A circuit of this type is shown in Fig. 5' and comprises a pair of triode electron discharge devices, which may be in asingle envelope. As usual in such circuits, only one of the twotri-odes is conductive at one time. In this circuit; the second triocle 62 is normal-ly conductive;:since its control electrode is biased positive with respect to its cathode. Current flowing therethrough and through resistance 63 biases'device 64'- tothe non-conductive condition.

Application of the'leading edge of a positive pulse as shown in linc'AIof Fig. 3 from the pulse frequency multivibrator-through the differentiating circuit comprising condenser 35 and resistor fi-fi-flres thedelay'multiyibrator 55 to transfer conauction fromthe second to the first triode, dee ping; atpositive output pulse on the anode 3 of the second triode, the pulse being shown on line D in Fig. 3. Conduction shifts back to the second triode to end the output pulse after an interval determined by the Values of the circuit components. The trailing edge of the positive pulses produced by the delay multivibrator fires a sweep timing multivibrator ll, the circuit of which is similar to that of the delay multivibrator iii except that the triodes will be so biased that the first, triode is normally conductive and the second triode non-conductive. The output or" the sweep timing multivibrator shown in line E of Fig. 3 is amplified and clipped in a clipper amplifi r E8 to convert the output to a square wave form indicated in line F of Fig. 3 and is then fed through a trigger amplifier I9 having an output indicated in line G of Fig. 3 with a sharp leading edge for firing the pulser 3 so that the V transmitted pulses indicated at |9a in line H of Fig. 3 occur precisely at the leading edge of the sweep timing multivibrator output.' As is apparent from 3, the time interval between the leading edge of the pulse frequency multivibrator output and the transmission of a pulse of radio waves is equal to the delay interval of the delay multivibrator [6. If more than one equip ment is tobe used in the same locality, interference can be prevented by adjustment of the delay intervals of the respective equipments, provided the delay interval is at least as long as one cycle of the sweep frequency. For example, another equipment might have its delay mulivibrator set to turn its sweep timing multivibrator on at the trailing edge of the output pulse of the sweep timing multivibrator of the present equipment.

Interference may also be avoided by externally synchronizing the pulse frequency multivibrator IS with a sine wave, each equipment being supplied with a diiferent phase voltage of the same sine wave synchronizing signal.

The sweep voltage is obtained from an oscillator having a resonant circuit consisting of an inductance 2!] and a variable condenser 2| coupled to a discharge device 22, the amplitude of the oscillations being adjusted by a slider 23 on a cathode resistor 24. The resonant circuit of the oscillator is tuned to a frequency such that the period of one complete oscillation is equal to the period of the sweep timing multivibrator output. The oscillator output is taken from opposite sides of the grounded center point of the inductance and fed through a push-pull amplifier 24a, 24b, to the vertical plates ID of the cathode ray tube. The horizontal plates II on the oathode ray tube are fed from a similar push-pull amplifier 24c, 25 connected to the oscillator output through resistance-capacitance phase shifting networks 26, 21 which efiect a 90-degree phase shift in the voltage fed to the horizontal plates. Because the voltages applied to the horizontal and vertical plates are displaced 90 degrees in time phase, the beam of the cathode ray tube is deflected in a circular trace if the amplitudes of the respective voltagesare made aqua-l by adjusting sliders 28 at the inputs of the push-pull amplifiers.

The sweep oscillator is synchronized with the :ransmitted pulses by a device 29 connected to ground through a branch circuit including part )f the inductance 20 and normally biased so as ;o carry sufficient current to damp oscillations n the sweep oscillator. The device 29 is con- ;rolled by applying to its grid 30 a negative pulse from the pulse frequency multivibrator l5 (2. nirror image of the positive pulse indicated in 4 line A of Fig. 3) which biases the device 29 to cut-off. The interruption of current through the device 29 causes an induced voltage in the inductance 20 which starts an oscillation in the resonant circuit Of the sweep oscillator which is continued at the level determined by the adjustment of the slider 23 on the cathode resistor 24. The oscillator output, as indicated in line B of Fig. 3, starts at the leading edge of the output pulse of the pulse frequency multivibrator and continues at constant amplitude throughout the output pulse. At the end of the output pulse the negative bias on the grid 30 is removed and the current through the device 29 due to its normal bias damps the sweep oscillation within a few cycles. Because the sweep oscillation is started by a transient due to the interruption of a current, the sweep oscillation always starts in the same manner and at'the instant of interruption. The sweep oscillation is therefore accurately synchronized with the leading edge of the pulse frequency multivibrator output. While the oscillator output builds up without any substantial delay,

there is a delay of the order of the one cycle in the building up of the voltages at the output terminals of the -degree phase shift networks 26 and 21, as indicated in line C of Fig. 3. Since the concentricity of the circular sweep depends upon equality of the voltages applied to the deflection plates ill and I, the first few cycles of the sweep oscillator voltage would cause a non-circular sweep trace. This is prevented by keeping the grid 3| of the cathode ray tube biased off during the delay interval of the delay multivibrator and 7 biasing the grid on during the sweep timing interval by connection to the output of the clipper amplifier E8. The transmitted pulses and the echoes, one of which is shown at 32 on line H of Fig. 3, accordingly appear on a circular sweep trace on the viewing screen of the cathode ray tube spaced apart in accordance with the range of the reflecting objects.

Since the accuracy of the range determination depends upon the frequency of the sweep oscillator, it is desirable that the frequency of the sweep oscillator be readily calibrated. This is effected by opening the switch 6 to disconnect the receiver 4 and by closing switches 33, 34, 35, 35a which respectively connect a crystal oscillator 36 to the pulse amplifier 1, short circuit the pulse frequency multivibrator I5, connect the grid 39 of the device 29 to a source of negative bias potential 3'! which biases the device off and permits continuous oscillation of the sweep oscillator, and connect thegrid 3| to a positive bias voltage. A circular trace modulated by the crystal oscillator frequency now appears on the cathode ray tube viewing screen as indicated at 38. The frequency of the sweep frequency oscillator is adjusted until the pattern produced by the crystal oscillator is stationary; then the sweep frequency is an exact submultiple of the crystal frequency. The diameter of the sweep trace can be adjusted by the sliders 28 which also must be adjusted to cause voltages of equal amplitude on the horizontal and vertical deflection plates. If these voltages are unequal, the sweep trace will be an ellipse with the major axis in line with the deflection plates to which the greater voltage is applied. If the phase difierence of the deflection voltages is difierent from 90 degrees, the major axis of the sweep trace will be inclined from the axes of the deflection plates. This results in a diagonal ellipticity which is corrected by adjusting the resistances 26 and 21. The concentrlcity of the sweep trace is adjusted by centering voltages. (not sweep timing multivibrator so the sweep timing interval is equal to 360 degrees of the sweep frequency, i. e.. so the sweep trace is :a full circle.

In Fig. '2 is shown locating equipment differing from that previously described in the use of a horizontal instead of a circular sweep for the range scale and in the manner of calibrating the range scale. Corresponding parts are indicated by the same reference numerals.

The sweep voltage is derived from a saw-tooth sweep circuit 39 fed from the clipper amplifier l8 and supplying to the horizontal deflection plates 1 i of the cathode ray tube a voltage which increases linearly during each sweep timing interval and abruptly decreases at the end of each sweep timing interval. The receiver output is applied through the switch 6 to the vertical -deflection-plat-es Ii] causing the deflections i2 rand L3 respectively corresponding to the transmitted pulses and the echoes and spaced in accordance with the range of the refiecting'objects.

The range scale is calibrated by an oscillator having a resonant circuit consisting of an inductance 4i! and a condenser 41 coupled to a device 42 :in such a manner as to sustain oscillations of a constant amplitude. The inductance :40 is in series with a device 33 (corresponding to device 29 in Fig, 1) having a grid 44 normally biased so as to cause a unidirectional flow of current through the inductance 4!! of sufiicient magnitude to damp oscillations. When the device i3 is conducting, a unidirectional current flows through the device 42. During the sweep timing interval, the device 63 is biased to cut-01f by a negative voltage from the sweep timing multivibrator, the negative voltage being a mirror image of the voltage fed to the clipper amplifier l8. The interruption of the current through the device 43 at the beginning of the sweep timing interval starts a transient oscillation in the resonant circuit 46, M which is maintained at the starting level by the device 42. The oscillation level is adjustable by a slider 45 controlling the bias of screen grid 46. At the end of the sweep timing interval, the removal of the cut-oil bias on the grid 4d causes a resumption of the flow of current through the device 33 to quickly damp the oscillations in the resonant circuit 40, 4|. The output of the oscillator is taken from a load resistor 41 and. fed to the grid 48 of a device G9 which functions as a clipper amplifier. In this device the negative halves of the sinusoidal voltage appearing at the load resistor 47 are clipped to a square wave shape which is differentiated by the inductance 5i) and resistance 5| and by the condenser 52 and resistance 53 to produce positive and negative peaks 5d, 55 coincident with the zero and 180 degree points of the oscillator output. The differentiated voltages are applied to the grid 56 of a device 5'? connected as a clipper amplifier. The negative peaks 55 have no efiect,

but the positive peaks are clipped and amplified causing negative pulse voltages 58 at the load resistor 59. The pulse voltages 58 occur at the beginning of each cycle of oscillation of the oscillator 40, M, 42, the first pulse occurring coincident with the negative voltage applied to the grid Mxatithe beginning ofthe sweep timing interval. Since the oscillator frequency is known the pulses SBlIIrOVideatimescaIe.

. The -.pulses$58 are used .to calibratethe range scale of the equipment by opening the switch .6 and 'aClOSingf-th switch .on a contact 766 connected to the :load resistor 59. This causes deflections Ed on :the :sweep trace of the cathode ray tube spaced apart from lett to right at intervals equal to 21318313813106. of :the oscillator, :the first deflection being coincident" with the transmitted pulses.

Since the time of travel of the pulses of radio waves :to and .fro mazreflectinglobject is a measure i of'its range, the. deflections 6i provide a range scale.

.inaboth sfonmsof .thednvention, the sweep oscillators-(2,0; 12;! 3f Fig. 1, 49,, ill, of Fig. 2) start oscillation synchronous with the keying impulses and without any transients. In each oscillator the transients are eliminated by having :the keying zdeyice :(39 .of *1, d3 of Fig. .2) cause the inductance and condenser of the oscillator circuit to have :a current Jan'dcharge prior to the keying impulse :corresp'onding. exactly to some part of the :Gycle .of the steady state oscillation. At the instant cf interruptiomof the current through the hosting devices, the resonant circuits of the oscillators areat steady state conditions and the subsequent oscillations :buildgup without any transients.

' The .keying circuit for the cathode ray display means is described and claimed iinni copending application Serial No .5:l2,3 0l, filed November-.30, 19%i3.

While I have rshown particular embodiments of my invention, it will be understood that many modifications may be made without departing from the spirit thereof and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a resonant circuit including an inductance, a discharge device coupled to said circuit so as to sustain oscillations, a branch circuit through said inductance in series with another discharge device normally carrying a unidirectional current sufiicient to damp oscillations in said circuit, means for keying said other device 01f whereby the induced voltage in said inductance starts oscillations in said circuit, a delay multivibrator keyed on by said keying means, a cathode ray tube normally biased off, a circular sweep circuit for said cathode ray tube utilizing said oscillations, and a sweep timing multivibrator keyed by said delay multivibrator for biasing said cathode ray tube on at the end of the delay interval of said delay multivibrator whereby said circular sweep starts at a point determined by said delay interval.

2. In combination, a multivibrator, a sweep frequency oscillator keyed by said multivibrator, acathode ray tube normally biased off, means excited by said oscillator for deflecting the cathode ray tube beam in a circular trace, delay means made operative by the leading edge of said first multivibrator output, and means for biasing the cathode ray beam on during the operative period of said delay means.

3. In combination, a resonant circuit including an inductance, a discharge device coupled to said circuit so as to sustain oscillations, a branch circuit through said inductance in series with another discharge device normally carrying a unidirectional current sufficient to damp oscillations in said circuit, means for keying ofi said other device whereby the induced voltage in said inductance starts oscillations in said circuit, delay means keyed on by said keying means, a cathode ray tube normally biased off, a sweep circuit for said cathode ray tube utilizing said oscillations, said delay means being arranged to bias said cathode ray tube on at the end of the delay interval of said delay means whereby the sweep starts at a point determined by said delay interval.

4. In combination, a resonant circuit including an inductance, a discharge device coupled to said circuit so as to sustain oscillations, a branch circuit through said inductance in series with another discharge device normally carrying a unidirectional current sufficient to damp oscillations in said circuit, means for keying off said other device whereby the induced voltage in said inductance starts oscillations in said circuit, delay means keyed on by said keying means, a cathode ray tube normally biased off,

a variable frequency sweep circuit for said cathg5 ode ray tube utilizing said oscillations, said delay means being arranged to bias said cathode ray tube on at the end of the delay interval of said delay means whereby the sweep starts at a point determined by said delay interval, and means for varying the duration of said delay interval independently of the variation of the frequency of.

said sweep circuit.

5. In combination, a resonant circuit including an inductance, a discharge device coupled to said circuit so as to sustain oscillations, a branch 8 circuit through said inductance in series with another discharge device normally carrying a uni-' directional current sufficient to damp oscillations in said circuit, means for keying off said other device whereby the induced voltage in said inductance starts oscillations in said circuit, a cathode ray tube normally biased off and having vertical and horizontal deflecting means, means for impressing said oscillations on one of said deflection means at 90 phase displacement with respect to the other of said deflection means, delay means keyed on by said keying means, said delay means being arranged to bias said cathode ray tube on at the end of a delay interval of sufficient duration to enable the voltages on said deflecting means to attain substantial equality whereby the sweep trace on the viewing screen of said cathode ray tube is substantially circular.

HARRY F. MAYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,103,362 Hansell Dec. 28, 1937 2,179,607 Bedford Nov. 14, 1939 2,265,848 Lewis Dec. 9, 1941 2,280,733 Tolson Apr. 21, 1942 2,313,966 Poch Mar. 16, 1943 2,370,685 Rea et al. Mar. 6, 1945 2,373,145 Sensiper et a1 Apr. 10, 1945 2,375,709 Thompson May 8, 1945 86 2,403,278 Hershberger July 2, 1946 

